1. Field of Invention
The invention is in the field of impact sensing detectors for use in metal forming impact presses and more particularly detectors which detect irregular operation of the press tooling with respect to a workpiece.
2. Description of the Prior Art
Metal forming impact presses are used to operate on strips of metal, termed herein the workpiece, so as to form the workpiece into desired parts such as contacts for electrical connectors. The tooling with which these presses are equipped provide the means for cutting, bending, forming, etc. the basic workpiece into the desired part, be it a contact or any other of an almost infinite number of different parts.
Press operation is constantly, semi-automatically monitored to detect and react to sensed malfunctions. Presses must be observed to assure that the parts produced conform to standards and also to assure that minor malfunctions do not go undetected leading to catastrophic machine or tooling failure. Such catastrophic failures are extremely costly in that machine or tooling repair or replacement is expensive. Further, machine downtime reduces the manufacturer's output.
For these reasons, workers in the art have expended much time and effort in attempts to develop reliable automatic devices to detect machine malfunctions and particularly with respect to devices which will produce early indicators of improper operation leading to serious malfunctions. Such indicators permit the machine operator to take corrective action before the severe malfunction actually occurs, thus preventing expensive repairs and long machine downtime.
An example of an impact press malfunction detector is described in U.S. Pat. No. 3,444,390 to Breidenbach et al. issued May 13, 1969. Breidenback et al. teach the basic concept that irregular operation of the tooling on a workpiece in a press can be detected by detecting the peak amplitude of the shock developed as the press dies contact the workpiece. The detecting mechanism comprises a suitable transducer such as a piezoelectric transducer which converts shock induced vibrations, that is the shock wave, into an electrical output correlatable to the shock.
Breidenback et al. recognized that, in the prior art, the shock analysis technique is limited to comparatively simple shock waves due to the confusion of signals which results when the nature of the shock forces become complex. They indicate that signal confusion is a particular problem in presses in which press tooling is caused to perform multiple functions, such as cutting and drawing all in one stroke. The solution set forth therein is to threshold compare a peak shock amplitude as represented by the peak voltage amplitude produced by the piezoelectric transducer to an adjustable sensitivity level of a latching amplifier after the piezoelectric resonant frequency has been filtered out.
While such an approach may work well to detect catastrophic press failures, it fails to give indications of minor malfunctions which may lead to more severe trouble. The present invention is an improvement over the Breidenbach et al. press impact sensor and operates to develop several warning indicator signals unrelated to peak voltages which may be used to automatically stop the press and give the press operator an analysis tool whereby he may pinpoint the malfunction.